The overall goal has been to study the mechanisms for the antimicrobial activities of bacitracin, polymyxins and EM 49. These three peptides are all membrane active peptides which affect membrane structure and functions. These antibiotics interact strongly with the membrane phase and in some cases, with specific membrane lipids. The peptides will be used to study lipid/peptide interactions by examining their interactions with membranes and model membrane systems. BIBLIOGRAPHIC REFERENCES: David LaPorte, Ken Rosenthal and Dan R. Storm, "Inhibition of E. coli Growth and Respiration by Polymyxin Covalently Attached to Agarose," Biochemistry (in press, 1977). Dan R. Storm, Ken Rosenthal and Paul Swanson, "Polymyxins and Related Peptide Antibiotics," Annu. Rev. Biochem. Vol. 46 (in press, 1977).